In the railway industry, there are standard service intervals and lifetimes for various components. The standard servicing interval for most components is nine years and the component is expected to have a lifetime of forty years. Railway cars also exhibit high usage compared to other land based forms of transport.
Conventional brake systems for railway cars are pneumatically driven and generally use diaphragm valves to control the application and release of pressure to the brake actuators. Considering the normal usage of a railway car, it is expected that the valve will have 44 million open/close cycles between services and a life time of 196 million open/close cycles. Diaphragm valves have been the preferred option historically due to their reliability and robustness, which permits the industry standard servicing intervals and lifetimes to be met.
However, for more modem systems, it is desirable to have electronic control of the brake system to permit new technologies to be introduced. One possibility is the use of a piston valve type arrangement, in which the piston position is toggled between two positions. To maintain the pressure in the valve, the piston is provided with piston rings. However, a significant problem with piston valves is that the wear on the surface of the piston bore and piston ring is high and in many cases leads to failure of the valve between servicing intervals.